1. Field of the Invention
Our invention relates to the processing of soft metals, and more particularly, to a method of rolling copper and copper alloys such as brass from a slab to a product of strip thickness.
2. Description of the Prior Art
Conventional rolling of soft metals such as copper, and copper alloys such as brass, is carried out by reducing a slab on a hot mill to a product of intermediate thickness. Thereafter, the intermediate product is quenched and the outer surface removed before being processed on a multiple stand cold mill to strip thickness. The cold rolled product of strip thickness is then annealed and finally chemically descaled and buffed or scalped. These processing lines are often extremely long and may require crossover facilities or other material handling equipment during processing.
The metallurgy of alloys of these materials is complex because of numerous phases formed on cooling from the melt, because alloy components have much higher vapor pressures than the parent alloy and because oxidation proceeds at and below the original outer surface (internal oxidation). All of these phenomena lead to an outer layer that is completely different than the interior of the slab to the extent that it is used as a sacrificial envelope that is removed by milling after initial breakdown of the slab. These phenomena are made more severe by processing the material in small batches.
Drawbacks to conventional processing lines and processes for these soft metals include substantial yield losses which come from the hot rolling process and subsequent milling prior to cold rolling. In addition, there is always the risk that surface imperfections are not properly removed and may be carried through to finished product. Further, the milling operation necessary for removing the outer surface of the hot rolled product results in a roughened surface which likewise may be carried through to the finished product. Conventional processing lines limit the slab sizes employed and the coil sizes generated from those slabs as a result of rolling limitations and quenching limitations of intermediate slab thicknesses.
The prolonged exposure of the slab being rolled to the atmosphere can result in selective evaporation of certain of the non-ferrous metals in the alloys and diffusion of oxygen into the subsurface. This explains the need for the milling operations following the quench.
The need remains for a compact processing line for soft metals such as copper, and copper alloys such as brass.